REFERENCE TO SEQUENCE LISTING
This application contains a Sequence Listing in computer readable form, which is incorporated herein by reference.
FIELD OF THE INVENTION
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The present invention relates to variants of an alpha-amylase having improved stability at an acidic pH and/or in the presence of strong chelators compared to its parent enzyme. Further, the invention relates to nucleic acids encoding the variants, methods of producing the variants, and methods for using the variants.
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OF THE INVENTION
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 18.104.22.168) constitute a group of enzymes, which catalyzes hydrolysis of starch and other linear and branched 1,4-gluosidic oligo- and polysaccharides.
There is a long history of industrial use of alpha-amylases in several known applications such as detergent, baking, brewing, starch liquefaction and saccharification, e.g., in preparation of high fructose syrups or as part of ethanol production from starch. These and other applications of alpha-amylases are known and utilize alpha-amylases derived from microorganisms, in particular bacterial alpha-amylases.
Among the first bacterial alpha-amylases to be used was an alpha-amylase from B. licheniformis, also known as Termamyl, which has been extensively characterized and the crystal structure has been determined for this enzyme. Alkaline amylases, such as AA560 (SEQ ID NO: 2), disclosed in WO 00/60060, form a particular group of alpha-amylases that have found use in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Termamyl and many highly efficient alpha-amylases required calcium for activity. In the crystal structure for Termamyl it was found that four calcium atom were bound in the alpha-amylase structure coordinated by negatively charged amino acid residues. This requirement for calcium is a disadvangtage in applications where strong chelating compounds are present, such as in detergents or during ethanol production from whole grains, where plant material comprising high amount of natural chelaters such as phytate is hydrolysed using alpha-amylases.
Calcium-insensitive amylases are known, e.g., the alpha-amylases disclosed in EP 1022334 and WO 03/083054, and a Bacillus circulans alpha-amylase having the sequence disclosed in UNIPROT:Q03657, but these amylases are inferior to many of the calcium-sensitive amylase when it comes to starch hydrolysis and starch removal in various applications.
It would therefore be beneficial to provide variants of a calcium-sensitive alpha-amylase with reduced calcium sensitivity compared to its parent enzyme.
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OF THE INVENTION
The present invention relates to isolated variants of a parent Termamyl-like alpha-amylase, comprising an alteration at two, three, four or five positions corresponding to positions 163, 188, 205, 208 and 209 of amino acids 1 to 485 of SEQ ID NO: 2 wherein the alteration(s) are independently
(i) an insertion of an amino acid immediately downstream of the position,
(ii) a deletion of the amino acid which occupies the position, and/or
(iii) a substitution of the amino acid which occupies the position, and wherein the variants have alpha-amylase activity.
The variants of the invention may further comprise one or more additional substitution(s).
Additionally, the isolated variants may comprise further alterations known to improve the performance of alpha-amylases including a deletion corresponding to amino acids 183 and 184 and substitutions in one or more of the positions 186, 193, 195, 202, 206, 214, 244, 452, 474 and 475, and each position corresponds to a position of the amino acid sequence of the enzyme having the amino acid sequence of SEQ ID NO: 2.
The variants of the invention have reduced calcium sensitivity compared with the parent alpha-amylase.
The present invention also relates to isolated nucleotide sequences encoding the variant alpha-amylases or polypeptides having alpha-amylase activity and to nucleic acid constructs, vectors, and host cells comprising the nucleotide sequences.
Methods for preparing the variants of the invention are also provided.
The present invention also relates to compositions comprising the variants of the invention, in particular a detergent additive composition, detergent composition, composition for manual or automatic dishwashing or compositions for manual or automatic laundry washing. Further, the invention relates to the use of an alpha-amylase variant according to the invention for washing and/or dishwashing, textile desizing and starch liquefaction. The invention also relates to a method for producing ethanol or other chemicals using the variant of the invention.
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OF THE INVENTION
Alpha-Amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 22.214.171.124) constitute a group of enzymes, which catalyze hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
cDNA: The term “cDNA” means a DNA molecule that can be prepared by reverse transcription from a mature, spliced, mRNA molecule obtained from a eukaryotic cell. cDNA lacks intron sequences that may be present in the corresponding genomic DNA. The initial, primary RNA transcript is a precursor to mRNA that is processed through a series of steps, including splicing, before appearing as mature spliced mRNA.
Coding sequence: The term “coding sequence” means a polynucleotide, which directly specifies the amino acid sequence of its polypeptide product. The boundaries of the coding sequence are generally determined by an open reading frame, which usually begins with the ATG start codon or alternative start codons such as GTG and TTG and ends with a stop codon such as TAA, TAG, and TGA. The coding sequence may be a DNA, cDNA, synthetic, or recombinant polynucleotide.
Control sequences: The term “control sequences” means all components necessary for the expression of a polynucleotide encoding a variant of the present invention. Each control sequence may be native or foreign to the polynucleotide encoding the variant or native or foreign to each other. Such control sequences include, but are not limited to, a leader, polyadenylation sequence, propeptide sequence, promoter, signal peptide sequence, and transcription terminator. At a minimum, the control sequences include a promoter, and transcriptional and translational stop signals. The control sequences may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the control sequences with the coding region of the polynucleotide encoding a variant.
Expression: The term “expression” includes any step involved in the production of the variant including, but not limited to, transcription, post-transcriptional modification, translation, post-translational modification, and secretion.
Expression vector: The term “expression vector” means a linear or circular DNA molecule that comprises a polynucleotide encoding a variant and is operably linked to additional nucleotides that provide for its expression.
Fragment: The term “fragment” means a polypeptide having one or more (several) amino acids deleted from the amino and/or carboxyl terminus of a mature polypeptide; wherein the fragment has alpha-amylase activity.
Host cell: The term “host cell” means any cell type that is susceptible to transformation, transfection, transduction, and the like with a nucleic acid construct or expression vector comprising a polynucleotide of the present invention. The term “host cell” encompasses any progeny of a parent cell that is not identical to the parent cell due to mutations that occur during replication.
Improved pH stability: The term “improved pH stability” is defined herein as a variant enzyme displaying retention of enzymatic activity after a period of incubation at a particular pH, which reduces the enzymatic activity of the parent enzyme. Improved pH stability may also result in variants better able to catalyze a reaction under such pH conditions.
Isolated variant: The terms “isolated” and “purified” mean a polypeptide or polynucleotide that is removed from at least one component with which it is naturally associated. For example, a variant may be at least 1% pure, e.g., at least 5% pure, at least 10% pure, at least 20% pure, at least 40% pure, at least 60% pure, at least 80% pure, and at least 90% pure, as determined by SDS-PAGE and a polynucleotide may be at least 1% pure, e.g., at least 5% pure, at least 10% pure, at least 20% pure, at least 40% pure, at least 60% pure, at least 80% pure, at least 90% pure, and at least 95% pure, as determined by agarose electrophoresis.
Mature polypeptide: The term “mature polypeptide” means a polypeptide in its final form following translation and any post-translational modifications, such as N-terminal processing, C-terminal truncation, glycosylation, phosphorylation, etc. It is known in the art that a host cell may produce a mixture of two of more different mature polypeptides (i.e., with a different C-terminal and/or N-terminal amino acid) expressed by the same polynucleotide.
Nucleic acid construct: The term “nucleic acid construct” means a nucleic acid molecule, either single- or double-stranded, which is isolated from a naturally occurring gene or is modified to contain segments of nucleic acids in a manner that would not otherwise exist in nature or which is synthetic. The term nucleic acid construct is synonymous with the term “expression cassette” when the nucleic acid construct contains the control sequences required for expression of a coding sequence of the present invention.